Censorship is the arbitrary or doctrinal limitation of one's freedom of expression. It goes through the examination of the holder of power over publications, plays, films or various works of art, before allowing their production and dissemination to the public.

Censorship designates various forms of attacks on freedom of expression and creation, before and / or after their dissemination (a priori and a posteriori censorship).

Political censorship (government limitation of freedom of expression) is different from indirect, unofficial censorship, but in the form of pressure, in particular a form of economic censorship (due in particular to media concentration, etc.) ; self-censorship phenomena can also be added.

• Eritrea
• North Korea
• Turkmenistan
• Saudi Arabia
• China
• Vietnam
• Iran
• Equatorial Guinea
• Belarus
• Cuba

The technologies used can be IP blocking by router, and DNS redirection. Governments can block web content that they dislike, yet still enjoy what they see as the Internet's benefits.

In December 2015, the HTTP error code 451 was formalized to allow websites to indicate when the content of a web page has been censored. However, several States prohibit its use, via an obligation of silence.

According to RSF, countries like Uzbekistan are creating modified mirrors. Thus, for the Internet user, access to the sites of political dissidents does not seem to be blocked.

The Uzbek authorities would copy the controversial sites and then modify them to undermine or weaken the prohibited positions. Uzbek Internet users accessing these sites then consult forged copies. This type of manipulation may be detected by an expert, but it is extremely difficult to detect by the average Internet user.